Palm Trees
Palm Trees Introduction
The Palm tree (Palmaceae) have
been termed the princes of the vegetable kingdom. Neither the
anatomy of the Palm tree stems nor the conformation of their
flowers, however, entitles them to any such high position in the
vegetable hierarchy. Palm tree stems are not more complicated in
structure than those of the common butcher’s broom (Ruscus);
their flowers are for the most part as simple as those of a rush
(Juncus). The order Palmaceae is characterized among
monocotyledonous plants by the presence of an unbranched stem
bearing a tuft of leaves at the extremity only, or with the
leaves scattered; these leaves, often gigantic in size, being
usually firm in texture and branching in a pinnate or palmate
fashion. The flowers are borne on simple or branching spikes,
very generally protected by a spathe or spathes, and each
consists typically of a perianth of six greenish, somewhat
inconspicuous segments in two rows, with six stamens, or pistil
of 1-3 carpel's, each with a single ovule and a succulent or dry
fruit. The seed consists almost exclusively of endosperm, Upper
portion of Coconut seed, albumen in a cavity in showing the
embryo, embedded in endosperm, which is lodged the relatively
very minute embryo. These are the general characteristics by
which this very well-defined order may be discriminated, but, in
a group containing considerably more than a thousand species,
deviations from the general plan of structure occur with some
frequency. As the characteristic appearances of palms depend to
a large extent upon these modifications, some of the more
important among them may briefly be noticed.
Palm Tree Stem
Taking the stem first, we may
mention that it is in very many palms relatively tall, erect,
unbranched, regularly cylindrical, or dilated below so as to
form an elongated cone, either smooth, or covered with the
projecting remnants of the former leaves, or marked with
circular scars indicating the position of those leaves which
have now fallen away. It varies in. diameter from the thickness
of a reed (as in Chamaedorea) to a sturdy pillar-like structure
as seen in the date-palm, Palmyra palm or Talipot. In other
cases the very slender stem is prostrate, scandent by means of
formidable hooked prickles which, by enabling the plant to
support itself on. the branches of neighboring trees, also
permit the stem to grow to a very great length and so to expose
the foliage to the light and air above the tree-tops of the
dense forests these palms grow in,’ as in the genus Calamus, the
Rattan or Cane palms. In. some few instances the trunk, or that
portion of it which is above ground, is so short that the plant
is in a loose way called “ stemless “ or “ acaulescent,” as in
Geonoma, and as happens sometimes in the only species found in a
wild state in Europe, Chamaerops humus. The vegetable ivory (Phytelephas)
of equatorial America has a very short thick stem bearing a tall
cluster of leaves which appears to rise from the ground. In many
species the trunk is covered with a dense network of stiff
fibers, often compacted together at the free ends into spines.
This fibrous material, which is so valuable for cordage,
consists of the fibrous tissue of the leafstalk, which in these
cases persists after the decay of the softer portions. It is
very characteristic of some palms to produce from the base of
the stem a series of adventitious roots which gradually thrust
themselves into the soil and serve to steady the tree and
prevent its overthrow by the wind. The underground stem of some
species, e.g. of Calamus, is a rhizome, or root-stock,
lengthening in a more or less horizontal manner by the
development of the terminal bud, and sending up lateral branches
like suckers from the root-stock, which form dense thickets of
cane-like stems. The branching of the stem above ground is
unusual, except in the case of the Doum palm of Egypt (Hyphaene)
, where the stem forks, often repeatedly; this is due to the
development of a branch to an equal strength with the main stem.
In other cases branching, when present, is probably the result
of some injury to the terminal bud at the top of the stem, in
consequence of which buds sprout out from below the apex.
The internal structure of the
stem does not differ fundamentally from that-of a typical
monocotyledonous stem, the taller, harder trunks owing their
hardness not only to the fibrous or woody skeleton but also to
the fact that, as growth goes on, the originally soft cellular
ground tissue through which the fibers run becomes hardened by
the deposit of woody matter within the cells, so that ultimately
the cellular portions become as hard as the woody fibrous
tissue.
Palm Trees and Their Leaves
The leaves of palms are either
arranged at more or less distant intervals along the stem, as in
the canes, or are approximated in tufts at the end of the stem,
I thus forming those noble crowns of foliage which are so
closely associated with the general idea of a palm. In the young
condition, while still unfolded, these leaves, with the
succulent end of the stem from which they arise, form “the
cabbage,” which in some species is highly esteemed as an article
of food.
The adult leaf very generally
presents a sheathing base tapering upwards into the stalk or
petiole, and this again bearing the lamina or blade. The sheath
and the petiole very often bear stout spines, as in the rattan
palms and when, in course of time, the upper parts of the leaf
decay and fall off, the base of the leaf-stalk and sheath often
remain, either entirely or in their fibrous portions only, which
latter constitute the investment to the stem already mentioned.
In size the leaves vary within very wide limits, some being only
a few inches in extent, while those of the noble Carycta I , may
be measured in tens of feet. In form the leaves of palms are
very rarely simple; usually they are more or less divided,
sometimes, as in Caryota, extremely so. In species of Geonoma,
Vers chaffeltia and some others, the leaf splits into two
divisions at the apex and not elsewhere; but more usually the
leaves branch regularly. The form of the segments is generally
more or less linear, but a very distinct appearance is given by
the broad wedge-shaped leaflets of such palms as Caryotct,
Martinezia or Mauritia. These forms run one into another by
transitional gradations; and even in the same palm the form of
the leaf is often very different at different stages of its
growth, so that it is a difficult matter to name correctly
seedling or juvenile palms in the condition in which we
generally meet with them in the nurseries, or even to foresee
what the future development of the plant is likely to be. Like
the other parts of the plant, the leaves are sometimes invested
with hairs or spines; and, in some instances, as in the
magnificent Ceroxylon andicola, the under surface is of a
glaucous white or bluish color, from a coating of wax.
The inflorescence of palms
consists generally of a fleshy spike, either simple or much
branched, studded with numerous, sometimes extremely numerous,
flowers, and enveloped by one or more sheathing bracts called “
spathes “. These parts may be small, or they may attain
relatively enormous dimensions, hanging down from amid the crown
of foliage like huge tresses, and adding greatly to the noble
effect of the leaves. In some cases, as in the Talipot palm, the
tree only flowers once; it grows for many years until it has
become a large tree then develops a huge inflorescence, and
after the fruit has ripened, dies.
Palm Tree Flowers
The individual flowers are
usually small (figs. 3, 6), greenish and insignificant; their
general structure has been mentioned already. Modifications from
the typical structure arise from difference of texture, and
specially from suppression of parts, in consequence of which the
flowers are very generally unisexual, though the flowers of the
two sexes are generally produced on the same tree (monoecious),
not indeed always in the same season, for a tree in one year may
produce all male flowers and in the next all female flowers.
Sometimes the flowers are modified by an increase in the number
of parts; thus the usually six stamens may be represented by
I2’to 24 or even by hundreds. The carpel's are usually three in
number, and more or less combined; but they may be free, and
their number may be reduced to two or even one. In any case each
carpel contains but a single ovule.
Owing to the sexual arrangements
before mentioned, the pollen has to be transported by the agency
of the wind or of insects to the female flowers. This is
facilitated sometimes by the elastic movements of the stamens
and anthers, which liberate the pollen so freely at certain
times that travelers speak of the date-palms of Egypt (Phoenix
dactylifera) being ‘at daybreak hidden in a mist of pollen
grains. In other cases fertilization is effected by the agency
of man, who removes the male flowers and scatters the pollen
over the fruit-bearing trees. This practice has been followed in
the case of the date from time immemorial; and it afforded one
of the earliest and most irrefragable proofs by means of which
the sexuality of plants was finally established. In the course
of ripening of the fruit two of the carpel's with their ovules
may become absorbed, as in the coco-nut, the fruit of which
contains only one seed though the three carpel's are indicated
by the three longitudinal sutures and by the presence of three
germ-pores on the hard endocarp.
Palm Tree Fruit
The Palm tree fruit is various
in form, size and character; sometimes, as in the common date it
is a berry with a fleshy rind enclosing a hard stony kernel, the
true seed; the fruit of Areca is similar; sometimes it is a kind
of drupe as in Acrccomia, or the coconut, Cocos nucif era, where
the fibrous central portion investing the hard shell corresponds
to the fleshy portion of a plum or cherry, while the shell or
nut corresponds to the stone of stone-fruits, the seed being the
kernel. In Borassus the three seeds are each enclosed in a
separate chamber formed by the stony endocarp. Sometimes, as in
the species of Metroxylon, Raphia, Daemonorops, &c,, the fruit
is covered with hard, pointed, reflexed shining scales, which
give it a very remarkable appearance.
Palm Tree Seeds
The Palm tree
seeds show a corresponding variety in size and shape, but always
consist of a mass of endosperm, in which is embedded a
relatively very minute embryo. The hard stone of the date is the
endosperm, the white oily flesh of the coco-nut is the same
substance in a softer condition; the so-called “vegetable ivory”
is derived from the endosperm of Phytelephas. In some genera the
inner seed coat becomes thickened along the course of the
vascular bundles and growing into the endosperm produces the
characteristic appearance in section known as ruminate—this is
well shown in the Areca nut.
Palm Tree Family
The order contains 32 genera
with about 1100 species mainly tropical, but with some
representatives in warm temperate regions. Chamaerops humilis is
a native of the Mediterranean region, and the date-palm yields
fruit in southern Europe. as far north as 38° N. latitude. In
eastern Asia the Palms, like other tropical families, extend
along the coast reaching Korea and the south of Japan. In
America a few’ small genera occur in the southern United States
and California; and in South America the southern limit is
reached in the Chilean genus Juhaea (the Chile coco-nut) at 37°
S. latitude. The great centers of distribution are tropical
America and tropical Asia; tropical Africa contains only 2
genera, though some of the species, like the Doum palm (Hyphaene
thebaica) and the Deleb or Palmyra palm (Borassusfiabellifer)
have a wide distribution. With three exceptions Old and New
World forms are distinct—the coco-nut (Cocos nucifera) is widely
distributed on the coasts of tropical Africa, in India and the
South Seas, the other species of the genus are confined to the
western hemisphere. The oil palm (Elaeis guineensis) is a native
of west tropical Africa, the other species of the genus is
tropical American. Raphia has also species in both tropical
Africa and tropical America.
The 132 genera of the order are
ranged under seven tribes, distinguished by the nature of the
foliage, the sexual conditions of the flower, the character of
the seed, the position of the raphe, &c. Other characters
serving to distinguish the minor groups are afforded by the
habit, the position of the spathes, the “aestivation” of the
flower, the nature of the stigma, the ovary, fruit, etc.
Palm Trees
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